Wireless communication devices, also known as, e.g., User Equipments (UEs), mobile terminals, wireless terminals, and/or mobile stations, operate in a wireless or cellular communications network or a wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed, for example, between two terminals, between a terminal and a regular telephone and/or between a terminal and a server, and is carried out via a Radio Access Network (RAN) and possibly one or more core networks comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
Examples of radio access networks include several standardized by members of the 3rd-Generation Partnership Project (3GPP), including: the Long Term Evolution (LTE) system, more formally known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN); and the Universal Terrestrial Radio Access Network (UTRAN), sometimes referred to as the UMTS Terrestrial Radio Access Network and often referred to as simply the WCDMA (Wideband Code-Division Multiple Access) network.
The UTRAN is one component of the Universal Mobile Telecommunications System (UMTS), which is a third generation mobile cellular technology for networks based on the Global system For Mobile (GSM) standard. UMTS employs Wideband Code Division Multiple Access (WCDMA) radio access technology to offer greater spectral efficiency and bandwidth to mobile network operators. UMTS specifies a complete network system covering the UTRAN, the core network (Mobile Application Part, or MAP), and the authentication of users via Subscriber Identity Module (SIM) cards.
More generally, a cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by an access node such as a base station, e.g. a Radio Base Station (RBS), which may be referred to as, for example, “eNB”, “eNodeB”, “Node B”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes, such as macro eNodeB, home eNodeB or pico base station, based on transmission power and also cell size.
A cell is the geographical area over which radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
Within a given RAN, multiple cells may be grouped into “registration areas.” In UTRAN, for example, these registration areas are referred to as UTRAN Registration Areas (URAs). These areas are designed to reduce the amount of signaling required between the network and inactive (but moving) terminals. A terminal moving from one cell to another cell that is within the same registration area is not required (as a general matter) to send an update (called a URA-Update, in 3GPP specifications for UTRAN), while a terminal moving from a cell in a first registration area to a cell in a second registration must notify the network (e.g., with a URA-Update message) that the registration area for reaching the terminal has changed. The implication of this behaviour is that the network does not know exactly where the inactive mobile terminal is, within the registration area, and must therefore broadcast any pages for the terminal from all cells within the registration area.
When the terminal needs to communicate with the network, e.g., when it has data to send or when it is paged by the network, it needs to notify the network (e.g., with a Cell-Update message) of the cell it is currently camping on in order to secure the necessary resources for the communication.
A concept of operational states has been incorporated in radio access technologies such as the 3GPP radio communication standards. In 3GPP systems operating according to WCDMA and LTE, the different operational states are called Radio Resource Control (RRC) states and include an idle state and several connected states. In WCDMA, there are five RRC states; Cell_DCH, Cell_FACH, URA_PCH, Cell_PCH, and Idle.
In a WCDMA system, a UE that has established an RRC Connection, i.e., a UE in UTRA RRC Connected mode, can be configured by the network to be in one of four connected RRC states at a given time: Cell_DCH, Cell_FACH, URA_PCH and Cell_PCH. The UTRA RRC Connected mode is further described in 3GPP Technical Specification (TS) 25.331 version 12.3.0. Each RRC state is characterized, among other things, by different achievable bitrates and cost in terms of resource utilization and energy.
A UE in CELL_DCH state, starting a web browsing session, will perceive a better user experience than a UE in other RRC states. If a UE is in other RRC states than CELL_DCH, a quick up switch to CELL_DCH will often improve the user experience by improving the screen response time and the total download time. However, unnecessary up-switches to CELL_DCH states should be avoided due to the higher cost of this RRC state in terms of network resources and UE battery consumption.
A wireless terminal that is sending only small amounts of data spends most of its time in a dormant state, so as to minimize the amount of power consumption. In a UMTS radio network, an inactive device may be configured to stay in the IDLE mode or one of the connected mode states URA_PCH, CELL_PCH, or CELL_FACH.
A wireless terminal in IDLE mode has no dedicated radio connection towards the RAN. There is also no dedicated connection for the terminal between the RAN and the Mobile Core Network (CN). As a result, connections need to be established before any data can be transmitted. The connection setup from IDLE mode begins with the wireless terminal making an autonomous transition to CELL_FACH state. The wireless terminal then initiates an RRC Connection Setup procedure to set up a dedicated radio connection. Next, a connection towards the CN is set up, which involves Authentication and Ciphering, Security Mode, and Radio Access Bearer Setup procedures, and possibly also a packet data protocol (PDP) Context Activation procedure, if one does not already exist. It is only then that the wireless terminal is able to transmit its data. Furthermore, after data transmission, the radio and CN connections need to be released before the wireless terminal can return to IDLE mode. This is illustrated in FIG. 1. Obviously, this procedure requires a lot of signaling, and may involve an inefficient use of network resources when small amounts of data are transmitted from time to time.
In connected mode, in contrast to IDLE mode, the wireless terminal does have a connection to the CN. There is, however, no dedicated radio connection for the states CELL_FACH, CELL_PCH, and URA_PCH. To transmit data in a cell, the wireless terminal needs cell-specific dedicated identities such as cell radio network temporary identity (c-RNTI), high speed downlink shared channel RNTI (H-RNTI), and E-DCH RNTI (E-RNTI) to identify itself. These cell-specific dedicated identities are unique to a given wireless terminal within a specific cell, but do not serve to identify the wireless terminal outside the cell. Wireless terminals that are in the CELL_DCH, CELL_FACH and CELL_PCH states are known to the RAN at the cell level. Wireless terminals in CELL_DCH and CELL_FACH are always allocated cell-specific identities, while those in the CELL_PCH state may or may not be allocated the identities. Wireless terminals in URA_PCH state are not known to the RAN at the cell-level, and are not allocated the identities.
A wireless terminal in the CELL_PCH or CELL_FACH state needs to perform a Cell Update whenever it moves into another cell. A wireless terminal in the URA_PCH state, on the other hand, can move around freely within the URA, which is usually made up of a significant number of cells. A wireless terminal that is inactive but moving is generally best served in the URA_PCH state, since this state does not require frequent signaling so long as no data is transmitted to or from the terminal.
Wireless terminals with cell-specific dedicated identities can send and receive data directly on the common channels for the CELL_FACH states, including the random access channel (RACH), the forward access channel (FACH), the common enhanced dedicated channel (common E-DCH), and the high-speed downlink shared channel (HS-DSCH).
Wireless terminals that do not have cell specific dedicated identities, which includes those terminals in URA_PCH state, must acquire the identities before sending or receiving data. This is done via the Cell Update procedure. For downlink data, the wireless terminal is first notified that data for the wireless terminal is available, using the Paging mechanism. The Cell Update procedure is illustrated in FIG. 2. In the Cell Update and Paging procedures, the UE is identified by its U-RNTI which is unique within the entire Public Land Mobile Network (PLMN). The U-RNTI is made up of a Radio Network Controller (RNC) ID and an S-RNTI.
The medium access control (MAC)-i and MAC-is protocols are used for transmission on common E-DCH in CELL_FACH. Each data transmission is accompanied by MAC-i/is headers. The MAC-i header includes information on the Logical Channel ID and the length of the MAC-is service data unit (SDU). When a wireless terminal is granted permission after random access to transmit on a common E-DCH, it starts by attaching its E-RNTI in a special MAC-i header called the MAC-i header 0. The purpose is to identify the wireless terminal and to perform collision resolution.
A collision occurs when two wireless terminals are trying to access at the same time using the same random access signature. Since random access is granted by signature, the network, intending to grant access to one wireless terminal, may have inadvertently granted access to both. Collisions are avoided by acknowledging the wireless terminal with an Absolute Grant (AG) sent on the enhanced absolute grant channel (E-AGCH). The AG contains the wireless terminal's E-RNTI, masked by a cyclic redundancy code (CRC), and information on the amount of data that can be sent. On reception of the AG, which is addressed to the wireless terminal via its E-RNTI, the wireless terminal knows that it has successfully acquired the common E-DCH. If the AG is not received within a certain amount of time, the wireless terminal would release the common E-DCH and try again.
The E-AGCH is a common channel that many wireless terminals can monitor at the same time. It carries the following information:                5-bit Absolute Grant Value: Indicates (via a power ratio) the amount of data the wireless terminal is allowed to transmit.        1-bit Absolute Grant Scope: Indicates if hybrid automatic repeat request (HARQ) process activation/deactivation should be applied to all HARQ processes or just the HARQ process pointed to by the AG.        16-bit CRC masked UE Identity (E-RNTI): Identifies the recipient of the AG.For the last field, a 16-bit CRC is calculated from the 6 bits of the AG Value and the AG Scope. The CRC is then used to mask the E-RNTI.        
HS-DSCH transmissions in CELL_FACH state are scheduled on the High Speed Shared Control Channel (HS-SCCH). The HS-SCCH includes the following transmission details: 7-bit Channelization-code-set info; 1-bit Modulation scheme info; 6-bit Transport Block Size (TBS) info; 3-bit Hybrid-ARQ process info; 3-bit Redundancy and constellation version; 1-bit New data indicator; and 16-bit UE Identity such as HS-DSCH RNTI (H-RNTI). Upon reception of an HS-SCCH transmission with the wireless terminal's H-RNTI, the wireless terminal knows, from the timing defined in the 3GPP specification, when to receive the data on the HS-DSCH.